Furnace.



A. P. STRNG.

FURNACE.

Hummm man me, s, 19u.

Patentd 0st. 9, 1917.

4 SHEETSSHEET 1 yUNITED STATES PATENT OFFICE;

ARTHUR P. STRONG, OF CHICAGO, ILLINOIS, ASSIGNOR T GREEN ENGrilllSlIEEBJNG 00M- PANY, 0F EAST CHICAGO, INDIANA, A. CORPORATION 0F ILLINOIS.

' FUBNACE.

Specification of Letters Patent.

Patented Oct. 9, 1917.

Application tiled Haren A6, 191'?. Serial No. 152,635.

To all 'whom 'it may concern:

lle' it known that I, AR'rHUn P. STRONG, n. citizen of the United States, residing at Chicago, in the county of Cook and State of illinois, have invented new and useful Iniprovernents in Furnaces, of which the foliowing is a specification.

This invention relates to improvements in toi-mines cf Steam boilers, and more particu- 'mi ly lo the construction of a furnace Stoker 1 s" "hr lnecl'lauical type, preferably embracan endless traveling chain grate and the inatures pertaining to means for supnir to the fuel bed supported upon tf1-atc, either in the 'forni of natural or `l draft.

in the opi-ration of steam boiler furnaces, the use of a forced draft is well recognized as desirable under variable load conditions, where the rapid promotion of combustion is noress-.iry to`inoet sudden increases of load upon the boiler. This is particularly true in boiler plants where the so-called peak loads must moet at certain )eriods of comparatively Short duration. lfrom tho etandpoint of economy and etlicienoy of operation, it is essential that the steaming capacity ofy the boiler be increased to meet 'the load. in the shortest interval of time. (in the 'other hand, it is equally essential, to etlicicnt and economical performance, no utilixe the natural draft under normal condilions of operation` thus mailing it unnernsffrxry to operato the forced draft fan or blower and tlux auxiliary operating units.

fit is' apparent, therefore, that a desirable arrangement the combination of both 'tori-cd und natural draft, together with moans for shifting from one to the other. Il i to such an arrangement that this invention relates and embodiesl a system of air ducts or passages located beneath the grate surface and commnnifating with Suitable supply ducts, together with dnmpers designor] to hc opened when the furnace is lu-in'g operated under forced draft, simultaneously closing the passages whereby the natural draft is supplied to tho grate suri'aco,` and. vivo versa', operati ve to close the forced draft ducts' andto permit the elitrancc of natural draft to the grate Surface. A preferable construction embodying the features of the invention is herein illustratcd and described in connection withy a socalled chain grate Stoker of the rernov.

able typo, that is, the Stoker unit being mounted '.on suitable trucks, thereby permitting the Stoker to be drawn out. from the furnace for the purpose of inspecting or the making, of repairs. A. Stoker of this type, togct ier with portions of the furnace necessary to a complete understandin of the invention, is herein described and ully illustrated in the accompanyingA drawings, in whirh i .Figure l is a view in longitudinal section of a furnace and Stoker embmlyinnV the features of the invention; i

Fig. 2 is an enlarged detail View in long'n tudinal section, taken on line Stm-2 of Fig. 4, showing the arrangement of dampers and operati ng devices;

Fig. 3 is a view in side elevation of one of the lateral air boxes removed, and show ing the arrangement of ducts and outlets therein;

Fig. Vlis a view in transverse section oi' the stolnifr, laken on line 4-1 o' Fig. 2;

Fig. 5 is a perspective View of one pair of cross-duets, showing dainpers and operating devices;

Fig. (i is an enlarged detail view of the damper operating members;

Fig. 7 is a detail view of the damper operating lowers; and

Fig. 8 if a detail view of the connectingV members between flic lateral air boxes and main supply duct, and showing the arrange ment of cont-rol (lampi-rs therein.

A steam boiler furnace of the type to which this invention is applicable, comprises the usual brick structure or setting, embracing side Walls 10, 10, a front wall 11 and a coking breast 12 extending inwardly Vand over the forward end of the fuel bed support 'n the grate, hereinafter to be described. earwardly of the front wall and centrally of the furnace, is a vertically extending, transverse bridge wall 13, the space intermediate the front Wall and the bridge Wall constituting,r the combustion chamber of the furnace. Above the combustion chamber are the boiler tubes 14 of the steam boiler, of the water tube type, said tubes being mounted at their ends in headers, the front header 15 being shown as supported immediately above the coking breast 12.

'Within the combustion chamber and exqsides of the stoker and general, two vertical side frame members 17,

having the form of longitudinally extending' plates .arranged in parallel. relation at the connected together by a plurality of transverse beams or girders 18, spaced apart at suitablel distances throughout the length of the side frame members.A The location and formation of these transverse girders will hereinafter be described in detail. The side frame members and transverse girdcrs form -the main gratemover,

supporting structure, which is, in turn, supported upon the floor or foundation of the furnace by means of trucks 19, located inwardly from the front and rear ends of the Stoker frame, and comprising' flanged wheels 20 mounted upon journal shafts 21, the latter being mounted in suitable journal bearings 22 provided along the lower edgesof the side rame members. The wheels 20 rest upon tracks 23, having thewform'of the usual T- rail, which extend throughout the length of the Ygrate and a suilicient distance outwardly Afrom the front of the furnace, thereby permitting the entire stoker to be removed from the furnace.

At the front and rear ends vof vthe Stoker frame are rotatably mounted sprocket shafts 24 and 25, respectively, said shafts being supported at their ends in suitable bearings formed in the side frame members 17, said shafts carrying a plurality of sprocket wheels 26, whiclimesh with the Ygrate and movably support the same. Mounted on the front sprocket shaft 24 is a gear wheel 27 (Fig. 1)', which meshes with a train of r duction gear wheels (not shown) mounted upon the stoker frame adj cent the front end of the grate, said gear train having operative connection with al suitable prim whereby power is through said gear train to rotate the front sprocket shaft, thus imparting movement to the grate in a direction to advance the fuel bed, supported upon the upper lead .of the grate,v in a direction from the front toward the rear of the combustion chamber. Intermediate the sprocket shafts and spaced at suitable distances apart throughout the length of the grate, 4are provided a plurality of transverse supporting rollers 28 and 29,

` A which support the upper and lower portions of the rate, respectivel 28 are Journaled in bearings 30 4) provided along the upper margins-o 'the side chain grate 16,

transmitted i The upper rollers' frame members, and the lower rollers 29 similarly journaled in bearingsl located above the lower margins of said side frame members.

The forward end of the stoker frame cornprises vertical side plates 32, located exv` terior of the'furnace and in the plane of the side frame members 17, said plates extending upwardly above the front end of the grate and in contact with the front wall ll. EX- tending between the.. side plates 32 is a front plate 33, supported in a downwardly inclined position and terminating above the grate surface, said front and side plates forming, with the front wall of the furnace, theI fuel hopper of the Stoker. The fuel hopper communicates with the mouth of the furnace, .formed between the lower face oi' the front wall and the surface of the grate, said mouth being capable of variation, as to size, by thc provisioi'i of a vertically movable gate 34, mounted above and in front of said mouth.

Adjacent the rear ond of the furnace are further provide stop members 35, 35, comprising vertically extending frames rigidly u mounted in the floor of the furnace adjacent each side frame member, each provided wi th an inclined and forwardly facing beam 3G adapted to engage a similarly inclined liange 37 on the outer faces of the side frame members. The stop frames are adapted to engage the stolrcrframe and to thus determine the position of the Stoker within the furnace by preventing the rearward movement of the stoker beyond its proper or predetermined position.

Referring now to the arrangement oi' the draft ducts embodying the features of the invention and associated with thc stclter, there are located in that portion of the grate within the combustion chamber, and between the upper and lower portions or leads of the grate, n plurality of transverse or cross-ducts, lsaid ducts being arranged in pairs, the ducts of each pair being associated with and separated by each of the girders 18,-as will now bc pointed out in detail. As shown in the drawings, there are four girders 18 within the space between 'the upper and lower leads of the grate and between the rear end thereof arid the front wall 11 of the furnace, each girder beinr located immediately below alternate ro 1ers 28, that is, the foremost girder extends downwardly in the vertical plane of the. roller just Within the combustion chamber, the second being similarl located below the third roller, the third gxrderrbeing located below the fifth roller 1n front, and the fourth girder being located adjacent to the rearmostroller. It asmuch as all of the Vair ducts illustrated Aare similar in construction, with the exception of the rearmost air duct, the description of the construction of one pair of ducts or unit will suffice for all. i

extend ing' tact `with the rollers- Referring to the fori'nation of the frontniost pair of cioss-iliuts (Fig. 2), the same are formed, as lit-,reinbefore suggested, by utilizing the girder lo, the same having a eross-sectioiuil coi'itour of an inverted T, comprising a wntiral web 38, which ternir natos substantially in contact with the under surface of the adjacent roller 2,8, and ex tends doivi'iwardlilf to a point just above the lower portion or earl of the grate, there being provided an integral transverse web B9 forwardly and rearwardly from the vertical web equal distances therefrom, the. outer margins` of said horizontal web be ing;` provided with short, upii'ardly extending flanges it?. hounlcrl on the upper mar i/'ins of the flanges 4U, al) of the` girdcr are iiainpcrs -l l, lil, comprising metal plates con neccd to said flanges by incans of hinges 'thi` dampen' ant-rfntcd at eithf-,r end of the lrausreiw web Li of tbe girder and on either ;iilc cl th vertical web 38 thereof, extends liaiisvci'scljv between the side frame members 17 and upwardly iii an inclined direction tow-.1rd cach other, terminating at ilu-ir upper margins in close proximity to each other, and, when in normal or closed position, as slim-rn in full lines in Fig. 2, bear against opposite sides of the associate roller From this descriiition it will be that there is formed on opposite sides of the vertical web BS of thc girder, a pair of .scp-mate air ducts 43., 4?, said vertical web forming ilur ,rear wall of cach duct., the horirontal web forming the bottoni wall of cach duct, and the dempers 111 forming the oaitci movable wall thereof, when in contact with the rollin lil Associated with the und and thi-:rd inverted T shaped girder i "e similarly for nit-.d pairs of air ducts @A4 and 415, ,413, respectively; likewise provided with hinged dampers 41, 41, identical with those heretofore described. The dampers L11, 41 of each pair of ducts are adapted to be swung simultaneously in a direction out- Ward'froni the adjacent roller and through an angle of substantially 45 to the dotted line position shown in Fig. 2, the movement of said dempers being limited by their con- 28, Q8, located intermediate the girdcrs 1S. The movement o the dempers to the dotted line position ef forts the openingV of the ducts to permit the admission o the forced draft to the grate,

if being cbserii'ed that when all of said daiiipers are in open position, that is, in

contact with the intermediate rollers, the...

space viiniluded between each pair of dem pers is enti rely shut off from communication with the space below the grate, and thus no air but that which is forced through the ducts can be admitted to the grate.

These dampers are operated by manually controlled devices, hereinafter described, al-

though the dempers associated'with each pair of ducts are controlled as a single unit and 'independeiitly of the other sets of dainers. p Referring to the rearmost duct 46, the saine is formed by the rearmost girder 18, which has a vertical web 40 oifset rearwardly from the adjacent roller and terminating in contact with the rear surface thereof and a single horizontal web, which extends for wardly from the vertical web 48, as before. rThe damper 41 of said rearinost duct is ol thc saine construction as before described', in fact, the duct is quite similar in all respects to a single duct of the pair of ducts heretofore described. liurtherinore, inasmuch as thc reai'niost girder 18 closes the draft delivery space of the grate, the vertical web terminates to the rear of thc roller and in contact therewith, as described, for the purpose of scaling said space from the open sparc to the rear of the fui-mice` Referring non' to the means cn'iployed for supplyiiig air to thc transverse cross ducts from a main source of supply, such as a blower or like apparatus located exterior of the furnace, there are provided longitudinally extending, lateral ducts or air boxes 50, 50, mounted on the Stoker frame and extending longitudinally along the outside of the side frame members 1T, 17, adjacent the ends of the cross ducts. These air boxes preferably comprise rectangular sheet metal conduits fastened against the outside surfaces of the frame members and extending from a point just forward of the front pair of cross ducts 4%, 43 rearwardly beyond the rear end of the grate, and adapted to have contact with the ,front surface of the bridge Wall 13, there being provided connections between the rear ends of the air boxes and a main supply duct, as will hereinafter be pointe out. The air boxes are divided into a plurality of Separate lon itudinal ducts, the corresponding ducts ov euch air box coniinunicating with the ends of each pair o cross ducts, as will bc understood from the following: and spaced below the top wall thereof, is a partition wall 51 (Figs. 3 and 4) extend'- ing throughout the length thereof and transversely between the vertical side Walls of the box, although inclined upwardly from the outer Wall thereof. In this manner there is formed above the partition wall 51 .a duct 52, which is closed at its outer en by the end Wall or closure 53. The duct 52 of each air box communicates with the ends 'of the front'pair ,of cross ducts ,43, 43 by means of o enings 54, 54 in the side frame members, w ich registerV with corresponding flanged openings 'in the air boxing. Below the partition wall 51 in each air ox 'is another partiton wall 55, also extending llon itudnally lof each air box and substantieJ ly `midway of the height thereof, said partition Mounted within yeach air boi);`

iso

, means of openings (S2 just beyond the next rearward wall 555 and partition wall 51 forming between them an air duct 56 extendin from the rear end of each air bog: to a point 'ust forward of the next rearward pair of cross ducts 45, 45, there being provlded just beyond said pair of ducts a vertical end Wall 57. Each duct icommunicates with its associated pair of cross ducts 44, 44 by means of an openinr 58 having 'a height equal to the distance etween the inner margins of the partition walls 51 and 55 and communi eating with the cross duct just below the upper 'duct 52. In the same manner, a third longitiulinal lduct llvis formed, by means (50, which extends vert1` of a partition wall cally upward from the bottom wall of each air box and is then inclined inwardly 'and upwardly, terminating:lr a short distance below the inner margin of the partition Wall 55, the air duct 51) thus formed haviuo' a somewhat irregular shape and exten ing forwardly from the rear end of the air box pair of cross ducts 45, 45. and being closed at its end by a vertical end wall (il. Each duct 59 communicates with its associated cross duets by l having a height equal to the distance between the inner edges of theipartition walls (i0 and 55. The remaining portion of each air box, inwardly and below the partition wall, forms a fourth duct .63, which is included between the partition wall 60 and the bottom and side walls of the air box, said duct extending forwardly from the rear end o-f the airbox a short distance beyond the rearmost-'eross duct 46, where it is closed by means of anend wall 64, saidrross duct being provided with an opening (i5 adjacent the lower portion thereof and having a height equal to the distance between the surface of the girder web 49 and the edge of the partition wall 60. i

'lhe rear ends of the air boxes 50. 50 commuinieate with amain snp ly duct 66 mounted transversely behind't e vertical bridge' y wall 13 and supplied with air f romn sultable blower mechanism, as hereinbefore i stated. As a means for connecting the air i boxes with the main'cross duct, there 1s emthe bridge Wall a connecting fitf Y removable bedded in ting 67 (Figs. 2` and 8) having the same cross-sectional arrangement of partition walls as the 'air boxes, and, in short, forming a continuation of said air'iboXes and air ducts therein. inasmuch as the Stoker is from thefurnace, it is desirable that the air boxes he removably connected at their rear ends to connecting fittings (i7, (i7 embedded within and extendingthrough the bridge wall, there being employed suitable flange connections, asat (i8, between the abutting ends of the.' air neetiug f ttings, ,whereby the'same can be disconnected |wlipnit is Aesired to withdraw the Stoker. from .fu'rnace. Within each rye 2,1.:

tative independently ,extends rearwardly to a point boxes and con- Vhave lateral extensions in the form of rods 70, preferably extending :through the side wall l() of the furnace, sind are provided with operating members operative from the exterior of the furnace, so that each damper or corresponding pairs of dampers can be manipulated independently of each other, thus permitting an' accurate Icontrol of the draft to each pair of erossjducts. Thus, when the furnace is being operated under forced draft, the amount of air supplied to the several portions of the grate area served by the several pairs of cross ducts, can be accurately regulated, and the firing conditions throughout the grate area can be controlled as desired. Y

Referring again to the several pairs of cross duets and the dampers associated therewith, it has been hereinbcfore pointed out that the darnpers associated with each pair of duets are adapted to be operated simultaneously with respect to each other, but independently of the dempers of the other pa irs of cross ducts. Asa preferable means for operating the several pairs of dampers, the followimgr construction is employed: Extending vlongitudinally beneath the gil-ders 18 and likewise' below the several cross duets, are a plurality of operating shafts, there being a single shaft for each pair of associated dani pers. i As a preferable arrangement, a telescopic construetion is employed; that is to say, tubular shafts, one inelosed within another and r0- of each other, are conneeted with the several pairs of dampers, each shaft extending from a common point at the forward end of the Stoker rearwardly to a point just beyond the dempers to. be o eratcd thereby. These shafts are prefera ly arranged as follows (Figs. 2, 6, and 7) The innermost shaft 71, preferably solid, beneath the rearmost girder 18, where it is supported in a bearing 72. Surrounding the shaft 71 is a tubular shaft 73, likewise extendin rearwardly but terminating just beyond the next forward pair of cross duets, said shaft being likewise jou'rnaled in similar beargirder 18 adjacent its end. rounding the tubular shaf as well as in shaft 74:, slightly greater in diameter and extending rearward y to a point just beyond the next pair of cross ducts, said tubular shaft 74 being journaled in bearings 72, as before. Surrounding the tubular shaft 74 is a still larger tubular shaft 75 extend- 'ing rearwardly just be ond the front pair of cross ducts and li rewise journaled in bearings 72 in the same manner as are t e other shafts. As already suggested, each shaft is operatively connecte to its associated pair of dampers, the following con struction being preferably employe 'or connecting each pair of dampers to its operating shaft. Mounted on each shaft is a lever arm 76, located immedialely -below cach damper and rigidly secured lto the operating shaft and connected to the damper (Fig. 5). Each damper is provide with an arm 77 extending outwardly therefrom at rightangles and preferably locate adjacent to the lower margin thereof. Connecting the cnds of the lever arm 76 and the arm 77 of the dempers is a link 78, preferably arranged in vertical position. y means of this form of connection it is ob served that by rotating one of the shafts in one direction the dainpers connected thereto will be swung outwardly from their closed position, and. by rotating said shafts in the opposite direction the dempers will be swung into closed position. As a preferable means of operating the damperbperating shafts independently of cach other, a series of con-- trolling levers are empl These levers are arranged as follows: As before pointed out, the forward ends of the shafts termi-- nate adjacent to the front end of the furnace and substantiall at the same point, although as a prefere le arrangement each shaft extends a short distance beyond the shaft immediatelysurrounding the same, thereby providing at the end of each shaft a bearin surface, -upon which is mounted a lever 9. These y d lby hand, the shafts being located preferably adjacent to one of the side frame members, thereby permitting access to the levers through a convenient opening in` the side frame members.

The operation and purpose of the construction herein described will be more clearly understood from the following: As is common in stakers of the type illustrated,

the ordinary stationary grate, the space below the activegrate surface, generally termed a free air space, communicates with the atmosphere through the front end of the furnace, and through this source delivers free air to the fuel bed. Where forced draft is used, 'it is desirable to shut oi the supply of free air or natural ft t0 the fuel bed and to deliver air under sure to the grate.

res- In the construct'i erein illustrated and described, this nir the active rate area and lower iads of the grate, and communicates with the at mosphere through the front portion of thc Stoker, in the usual manner, drawn upwardly through the lower lead o the grate and into the space between the up per and lower leads and thence to the fuel ed. The arrangement. of the girders, to gether 4with the hinged dempers, below the grate, provides in effect a series of spaces or chambers located in the free air space and inclosed by partition walls in the 'form of the girder webs and dempers. These spaces or throughout ducts, which connnunicato with sources of y' l forced draft, may be entirely inclosed or shut olf from the free air space, by moving the dempers into closed position, time` ren dering them inoperative. By svfmgingy` the dempers :to open position, forced draft spaces or ducts are not only opened to permit the delivery of air under pressure to the grate, but the entire free air Space is converted into a forced draft space, the dampers forming a partition wall. shut ting off the space below the grate from the source of free air. The conversion of the .free air space into forced draft il it is to be noted, is accomplished without nution of of air uniformly throughout the grate arca, this being due to the novel arrangement et the pairs of ducts, which permits them to open in a manner likened to the opening of a number of fans spaced apart end to end, whereby the area or air space is merely re arranged so as to supply it with air from either a source of natural draft or a source of forced draft.

By reason of the damper controlling mechanism, it is pos Y sible to operate the furnace under both not ural and forced draft, by simply opening dempers of one or dempers, retaining the remainder 1n This mode of operation is often desirable, where the combustion in certain portions of the grate area is such as to require an in creased draft, as for instance where the fuel bed is thicker, or for other reasons whic make the natural draft insuiicient to promote proper comb v The principal of a construction such herein described lie chieiiy in the simplicity and low cost of construction, inasmuch' as the permanent elements of the 'lized to form a large Stoker frame are uti portion of the ducts, for instance the cross ders 1g pf the ducts consist largely of stoker frame, the dempers to form the ducts. The further advantage is the simplicity of operation and performance of the dempers, in at an' arrangement of rotative shafts, connecting levers, and links is only necessary for the opthe air being f howewmf, the

the space available for the delivery the 'independent operation of s;

closed position. `j

eration of said dempers. Here, again, the permanent members of the Stoker are utilized to aid in the functioning of the darnpers, namely, the rollers, which serve as bearing membersfor the dempers and also to seal the air spaces formed by said dempers, thereby eliminating the additional bearings or sealing members, as well as a more positive type of operatingr mechanism to effect th(l closing and sealing-of thc ducts and air spaces.

Although the novel construction is embodied in a r-liaingrate Stoker of the removable typo. it is apparent that the same construe` tion is applicable to a Stoker of the non-reinorabh typo, and cven to the ordinary stationary grate. As regards the removable type ofy stoker.tlie addition of the cross ducts' and longitudinal ducts interferes in no way wil. 'i the removable Stoker, inasmuch as the air boxes are easily disconnected at their reni' ends from the main duct and thc Stoker drawn out from the furnace in the usual way.

Owing to the adaptability of this invention to all types of furnaces, as hereinbev 'fore set forth, and for the reason that the construction herein described and illustrated may be modified without departing from the spirit of' the invention, it fis not desired to limit this invention, except in so far as set forth in the appended claims.

I claim as my invention: y

l. In a furnace, the combination 0f a grate provided with a free air space therebelow, a plurality of forced draft ducts in said free air space, dempers normally closing said forced draft ducts and located in opposed relation to each other, said'dainpers being :notable toward cach other in said free air space andndaptcd to form a parti- -zion wall shuttinfif` oil'.the space between said forced draft ducts from communication with :i source of free air.

2. In a furnace, the combination of a grate, a plurality of forced draft ducts extending transversely and arranged in spaced relation beneath 'said girate,- there being provideda free air space between said ducts, and a damper associated with each of said forced draft ducts, adapted to be moved in thereto.

a direction toward each other to close said free air `space.

In a furnace, the combination of a gr-ate, a plurality of forced draft ducts arranged in parallel and spaced relation beneath the grate, there being provided free Aair spaces intermediate said duets, the latter heine; provided `with oppositely disposed openings, and dempers normally closing said openings from communication with Vsaid `free air spaces and movable in a direction.

toward each other and into saiid'free air spaces to shut ntl the supply of free air /sald air space, and means for 4.111 a furnace, the combination of a grate, a plurality of forced draft duets extending trensversel and arranged in spaced relation throughon the grate, there bein provided free air petssages between sai; ducts communicating with said free nir space, said ducts being provided with oppositely disposed openings and dampers mounted on said ducts and normally adapted to close said openings and to be swunV outwardly toward each other, to close saidg free air assages.

5. In a furnace, he combination of a grate, a plurality of parallel Giiilcl's extending beneath said grate and in the free air space therehelow, a pair of cross ducts assoprising vertically arranged on opposite sides of each grder, said dumpers being movablelto open said Icross ducts to comn'iunication with said free air space and into a position to shut off the supply of free air to said air space, and means for supplying forced draft to said ducts. I

In a furnace, the combination of a grate, a supporting;r girdcr extending,1r transversely beneath said grate and comprising a vertical web and a horizontal web, a .vertically arranged damper hinged to the margin of said horizontal web and in one' position inclined toward the vertical web of said glrder to provide an inclosed duct and mov- 4 able away from said vertical web to open communication with a free lair space beneath said grate and close the latter from oommnnication with a source of free air, and ieans for supplying forced draft to said 7. In a furnace, the combination of a traveling grate, a supporting roller engag ing the under surface 'of said grate, a plurality of forced draft ducts beneath said grate and on opposite sides of saidsupporb ing'roller, said ducts having oppositely disposed openings ad-aptedto communicate with a free air space intermediate Said ducts, and dempers normal] and movable towar each other and into contact with said supporting roller to close said air space. i i

8. In` a furnace, thel combination of a grate, a plurality of parallel girders extendlng beneath said grate and ina Vfree air space therebelow und provided with laterally, extending webs, vertically arrangedl dempers hinged upon the ou'ter margins of said webs, said dampersbein adapted to be swung into one position to position to shut off'the supply'of free4 air to su 1 in forced draftto seid ducts. Jg

9. In n. furnace, the combination of a traveling grate, transverse supportingrollelated with nach of said girders and com dampers hinged .closing said openings" u rm a.' duct ad# jacent each of sind girders 'and into another' 'ers spaced apart bepeath sedgrate,forced 13o te, Y '7 chain grate, a Sugg-perdu frame comprising ci: said vin??? pknsity of rollers snpyms'ting Suk? gram ilwm beng a, roller 'wanted in viiivffal alnmnnt Wilzlemeh of .said ggrdms am@ i: Pnn-r immun/dime smid gircras? u plnniy m" rau'xpers hinged to he holznntal wens ni nach girder and ininsfd upwardy in bearing engagument with the anlm-s udaccnt nach girder, und means for swinging Suid dampers outwardly from eontac with said last mentioned mllers and infn neming engagement with the. inmunedntc 'nvrs.

15. fmnnce tollzuefq compsfsing :1 tljaving chain grate'. u gfnte sl'pm'urg ilanw mmmw wi'hn may. Eu-nume, wir tnnesili relineaerswv nf @aid frame w up; n? und Vfwvefr af gli :ne nir 1:1136; mtmfing nngtud V "f frzmw and fnruvicnd with n .is niv. passages), nach communi pnmug cat-ing wn sepan-nti) crass ducts, a, main air supply duct, xex in the furnace and provided wh an outlet. opening nnnnniating frame. (1in an* box exfenimg ngtudinally.

one und of Said grate, and n main supply dut permanently mounted in the furnace {my} having demchnble connection with Said air bmx,

h1 testimony tm; I claim the foregoing msance Gf fawn wit'nessen, th's 1st day of durch, A. Ds 1917.

ARTHUR P. STRONG. Witnesses:

mzxwnnn Bunn, Jr., HERMAN TGRHENTGN, 

